With the advent of widespread use of cellular telephones and the corresponding growth of wireless subscribers for using such telephones, a need has arisen for maximizing a network's capacity within an existing communication infrastructure. Before describing how this need has been addressed, however, a general structure of a communications system will be described. The infrastructure of a communications network generally includes multiple mobile switching centers (MSCs) which provide control, tracking, and data about mobile users within a predetermined area.
A distributed home location register wireless network architecture is typically utilized to establish an infrastructure for a wireless communications network. In such an architecture, the home MSC tracks and determines where the mobile user is currently registered. A mobile user is registered on a home location register (HLR) within a home mobile switching center (MSC). When the mobile user travels away from their home MSC, the mobile user is detected by a second mobile switching center. The second mobile switching center then provides information to the home MSC. The home MSC registers the location of the mobile user on a visiting location register (VLR) within the MSC visited.
Subsequently, when a call is received by a current MSC, the current visited MSC determines whether or not the mobile user to whom the call is directed is registered in the HLR or is registered in the VLR. If the mobile user is registered in the VLR, the home MSC transmits information to the mobile user's current MSC. Through this method, the home MSC is able to transfer the call to the current MSC so that the mobile user receives the call even when they are not within their own home MSC.
In such a distributed wireless network architecture, the mobility of subscribers is a significant factor in resource allocation and has a tremendous impact on network capacity since a subscriber must be located on a regular basis to indicate whether or not that user should be registered on a home location register or a visiting location register. Given the demands made on an MSC in making this determination, it is possible for some mobile switching centers to be heavily loaded, while others are lightly loaded due to an ad hoc distribution of subscribers. Such an uneven loading results in a poor overall network performance because some MSCs are functioning at their maximum capacity and expending all of their resources, while other MSCs are barely being utilized at all. Without an even distribution of resources, it is difficult to achieve maximum effectiveness and, hence, the maximum user capacity of an existing network.
Improving network performance by balancing a load on each of the MSCs in a communications network has piqued considerable interest by the communications industry. Typically, the problem of a load in a communications network balancing is categorized as a resource allocation problem where a control variable is an "assignment policy." While an objective of resource allocation varies with the application to which it is being applied, often the underlying idea is allocating a total load across multiple resources as evenly as possible. Three main types of load balancing problems have been studied by numerous authors. In an article entitled "Heuristic Algorithms for Adaptive Load Sharing in Local Networks," published in Systems Integration, pp. 762-770 in 1990, Schaar, et al. apply heuristic techniques to solve the load balancing problems. Additionally, Kunz in "The Influence of Different Workload Descriptions on a Heuristic Load Balancing Scheme," published in IEEE Transactions on Software Engineering, Vol. 17, No. 7, pp. 725-730, on July 1991, also implement heuristic techniques to solve such loading problems. In an article entitled "On Simple Algorithms for Dynamic Load Balancing," published in Proceedings of IEEE INFOCOM, Vol. 1, pp. 230-238, 1995, by Alanyali et al. incorporates finite capacity constraints on resources to solve this loading problem. Additionally, another technique developed by Kremien et al. considers information dissemination in allocation decision-making in their article on load balancing entitled "Methodical Analysis of Adaptive Load Sharing Algorithms," published in IEEE Transactions on Parallel and Distributed Systems, Vol. 3, No. 6, pp.747-760 of November 1992. It should be noted, however, that terminal or subscriber mobility issues were not considered in any of the above-mentioned studies. Therefore, the studies mentioned above fail to provide an adequate solution for balancing the loads amongst mobile switching centers, as the mobility of subscribers is not accounted for.
Therefore, it is desirable to have a load balancing strategy which accounts for mobility of subscribers in a communications network so that the existing communications infrastructure may be more effectively and efficiently utilized.